During infection, the bacterial pathogen Listeria propagates by an unusual direct cell-to-cell spread strategy. This behavior, also seen in Shigella flexneri and Vaccinia virus, shields the pathogen from the host immune system. In order to effect cell-to-cell spread, L. monocytogenes induces uptake of portions of infected cells by nearby host cells through a poorly understood process which appears to be related to phagocytosis. The investigator proposes to characterize the role of the host cell during bacterial spreading in order to better understand pathogenesis and to elucidate the process of phagocytosis in general. To do so, he will first examine the potential role of proteins thought to participate in phagocytosis, with an emphasis on the actin cytoskeleton. Proteins will be assessed for their colocalization with spreading bacteria using immunofluorescence. He will use proven dominant negative forms of two prominent candidate regulators of phagocytosis, dynamin and clathrin, to test their roles in the pathogenic process. Last, he proposed a somatic cell mutagenesis to identify other candidate mediators of L. monocytogenes spread.